The present invention relates an improved method and apparatus for controlling the air quality in the fiber forming zone of glass fiber manufacturing operations. The process of glass fiber forming is regularly plagued by the catastrophic breaking of the glass fiber filaments between the bushing of a glass melt furnace and the applicator which supplies a binder and/or size to the filaments. It is well known that a large percentage of all filament breakage occurs in the fiber forming zone. If the production of clear and cordy beads are included in the count, then approximately one-half of all process failures occur between the bushing and the applicator. Identifiable stones are the cause of approximately one-fourth of the total breaks and mechanical and people caused breaks produce the last one-fourth. Past efforts to reduce breakage have emphasized causes and cures to effect a reduction in the identifiable stones and mechanical and people caused breaks. The present invention emphasizes conditioning of the fiber forming environment to reduce the incidence of filament breakage in the zone between the bushing and the applicator.
A large number of variables are present in the fiber forming process which tend to create a condition that encourages catastrophic filament breakage in the fiber forming zone. A partial listing of such process variables includes bad binder mixes, rough aprons, unacceptable fan tension, alignment problems in the fiber forming apparatus, thermal irregularities, air balance problems, prepad spray imbalances, and temperature and humidity imbalances. A great deal of attention has been paid to the control of temperature and humidity of the fiber forming environment. For instance, the Bour patent, U.S. Pat. No. 4,146,377 has identified non-uniform thermal conditions in the fiber forming environment as a cause for filament breakage. Bour states that changes in the velocity or air temperature near the molten streams of glass can change the viscosity and tension of the streams sufficiently to break the filaments. Bour states that if the air flow in the fiber forming zone is erratic in either velocity or temperature, filament breakage will occur due to the changes in air velocity and/or air temperature. As a result, Bour developed a method for eliminating such erratic air flow and air temperatures immediately below the bushing tips and providing more uniform air flow and air temperatures in the fiber forming zone.
The intrusion of high particulate fluxes into the fiber forming zone has also been identified as another primary cause of increased break performance and surface flaws in the forming glass fiber filament. Air-borne particulate in the fiber forming zone, such as fly and fuzz, can have a catastrophic effect on the formation of the glass fiber filaments. The effects of such air-borne particulate is sensitive to the flux of the particulate which is defined in terms of the number of particles passing through a unit area in a given unit time. Flux determines, when viewed in light of the number and surface area of the forming cones in a given fiber forming tunnel, the probability that a collision between the filaments and the air-borne particulate will take place. Since the particulate is air-borne, its velocity is determined by the air being pulled into each fiber forming zone contained in the forming tunnel.
The size distribution and chemical nature of the particulate depends primarily upon the source of the particulate. Common sources of air-borne particulate which have a deleterious effect on fiber forming are: fly (broken glass filaments) from forming breaks and fabrication operations, Ti.sub.2 from gelcoat production, sodium iron laden sized droplets, cement dust from tunnel forming floors, soil dust and batch dust. The concentration of such air-borne particulate in the fiber forming environment is further effected by the activities related to various outside sources and by the effectiveness with which particulate removal occurs prior to outside air becoming tunnel air. In the past, efforts have been directed to eliminate the outside particulate flux by filtering tunnel air and utilizing air conditioned or HVAC air directed at the bushing in the fiber forming zone. Such efforts have not resulted in completely successful results.
It is an object of the present invention to provide an improved method and apparatus for controlling the fiber forming environment in a glass fiber forming operation.